How important are post-interview thank-you notes?

About 15 percent of the 650 hiring managers in a recent CareerBuilder survey said they wouldn't hire someone who failed to send a thank-you note after an interview. Another 32 percent said they'd still consider the candidate, but would think less of him or her. Speed is also important: 26 percent of hiring managers say they expect to receive a thank-you note within two days after the interview, and 36 percent expect to have it within five days.